Pi-allyl-palladium compounds have been reported in the literature and have been found useful as chemical intermediates and catalysts. Such compounds have gained increasing importance as catalysts for reactions of olefins and other unsaturated organic molecules, for example, processes of oligomerization. Additionally, such compounds have found use as catalysts in the cyclo-oligomerization of mono- and diolefins. For example, pi-allyl-palladium compounds can be used successfully as catalysts for the cyclo-oligomerization of 1, 3-diolefins, particularly butadiene, to produce cyclododecatriene.
Although the pi-allyl-palladium compounds have been known to be useful catalysts in the types of reactions expressed herein, there has been some difficulty in obtaining these compounds in sufficiently high quantities to make them practically available for commercial organic synthesis operations. This is so because the pi-allyl-palladium compounds are frequently difficult to isolate from reaction mixtures and are quite often obtained in very low yields.
Moreover, in many prior processing methods of preparation of pi-allyl-palladium compounds, the general approach has been to first synthesize the entire organic structure of the desired pi-allyl-palladium compound and thereafter, as a last processing reaction step, to complex the organic structure with a palladium salt. Such methods have only met with limited success. Many of the reactions produce the desired organic structures only in limited quantities, with numerous side products, and require rather severe reaction conditions, carefully controlled to within well-defined limits. In addition, many of the prior art reactions which first involve formation of the organic moiety and thereafter complexing that moiety with the palladium, involve reactions which are not tolerant of substituted functional groups on the organic moiety.
Accordingly, it is the principal object of this invention to provide a method of synthesizing pi-allyl-palladium compounds wherein the desired pi-allyl-palladium compound is formed by reacting two organic molecules of relatively simple structure with a palladium (II) salt wherein a carbon-to-carbon bond is formed between the two organic molecules, with the resulting organic moiety complexing with the palladium to provide the desired pi-allyl-palladium complex.
In addition, it is an object of this invention to provide a reaction which can be run under mild conditions, which yields the desired pi-allyl-palladium compounds in high yields, often in excess of 80%, and in many cases, in excess of 90%.
Yet another object of this invention is to provide a reaction which will yield the pi-allyl-palladium compounds, with the reaction being tolerant to functional groups positioned on one or more of the organic reacting reagents, without adversely affecting the reaction.
Still another object of this invention is to provide a process of preparing pi-allyl-palladium compounds which meets each of the above-mentioned objectives by reacting a vinylmercuric salt and an olefin, preferably a terminal bond-containing olefin, with a palladium (II) salt.
The method of accomplishing these and other objects of the invention will become apparent from the following detailed description of the invention.